Water infiltration influenced by agroforestry and grass buffers for a grazed pasture system

Agroforestry (AgB) and grass buffers (GB) are often adopted as alternative resource management tools in agroecosystems for environmental and economic benefits. The objective of this study was to compare the influence of AgB and GB systems under rotationally stocked (RP) and continuously stocked (CP) pasture systems on water infiltration measured using ponded infiltration and tension infiltration methods. Buffers were surrounded by a fence that prevented cattle from grazing within these areas. Soils at the site are Menfro silt loam (fine-silty, mixed, superactive, mesic Typic Hapludalf). Infiltration rates were measured using ponded ring infiltration units during 2 years for the four (AgB, GB, RP and CP) treatments with three replicates from two subareas within each treatment. Infiltration rate as a function of tension (at 50, 100, and 150 mm) was also measured using a tension infiltrometer. Water infiltration parameters were estimated using Green-Ampt and Parlange infiltration equations. Quasi-steady state infiltration rates (q _s ) and field-saturated hydraulic conductivity (K _fs ) for buffers were about 31 and 46 times higher as compared to pasture treatments, respectively. Green-Ampt and Parlange models appeared to fit measured data with r ² values ranging from 0.91 to 0.98. The q _s (measured with ponded method) in the first year for the GB treatment was the highest (221 mm h⁻¹) and for the CP treatment was the lowest (3.7 mm h⁻¹). For both years, estimated sorptivity (S) and saturated hydraulic conductivity (K _s ) parameters were higher for buffer areas compared to the stocked pasture areas. Grazing reduced the infiltration rate for the pasture (RP and CP) treatments. Results show that the buffer areas have higher infiltration rates which imply lower runoff compared to pasture areas.     

Root length density and carbon content of agroforestry and grass buffers under grazed pasture systems in a Hapludalf

Enhancement of root development helps to improve soil physical properties, carbon sequestration, and water quality of streams. The objective of this study was to evaluate differences in root length density (RLD) and root and soil carbon content within grass buffer (GB), agroforestry buffer (AgB), rotationally grazed pasture (RG) and continuously grazed pasture (CG) treatments. Pasture and GB areas included red clover (Trifolium pretense L.) and lespedeza (Kummerowia stipulacea Maxim.) planted into fescue (Festuca arundinacea Schreb.) while AgB included Eastern cottonwood trees (Populus deltoids Bortr. ex Marsh.) planted into fescue. One-meter deep soil cores were collected from each treatment in August 2007 and 2008 with a soil probe. Three soil cores were sampled at six replicate sampling positions. Soil cores were collected in plastic tubes inserted inside the metal soil probe. Soils were segregated by horizons, and roots were separated into three diameter classes (0–1, 1–2, >2 mm) by soil horizon. Root length was determined using a flatbed scanner assisted with computer software. Buffer treatments (167 cm/100 cm³) had 4.5 times higher RLD as compared to pasture treatments (37.3 cm/100 cm³). The AgB treatment had the highest (173.5 cm/100 cm³) RLD and CG pasture had the lowest (10.8 cm/100 cm³) value. Root carbon was about 3% higher for the buffers compared to RG treatment. Soil carbon was about 115% higher for the buffers compared to pasture treatments. Results from this study imply that establishment of agroforestry and GB on grazed pasture watersheds improve soil carbon accumulation and root parameters which enhance soil physical and chemical properties thus improving the environmental quality of the landscape.     

APEX model simulation of runoff and sediment losses for grazed pasture watersheds with agroforestry buffers

Buffers have been found to reduce non-point source pollution (NPSP) from watersheds. Hydrologic simulation models assist in predicting the effects of buffers on runoff and sediment losses from small watersheds. The objective of this study was to calibrate, validate and simulate runoff and sediment losses and compare buffer effects on NPSP losses relative to control watersheds (no buffer) for seven years. The experimental design consists of four watersheds under pasture management which were monitored from 2002 through 2008; two with agroforestry buffers (AgB 100 and AgB 300) and two control watersheds (CW 400 and CW 600). Pasture areas included red clover (Trifolium pretense L.) and lespedeza (Kummerowia stipulacea Maxim.) planted into fescue (Festuca arundinacea Schreb.) while the agroforestry buffer area included Eastern cottonwood trees (Populus deltoids Bortr. ex Marsh.) planted into fescue. The APEX model was calibrated from 2002 to 2005 and was validated from 2006 to 2008. The r ² and NSE values for the calibration and validation periods of the runoff varied from 0.52 to 0.78 and 0.50 to 0.74, respectively. The model did not predict sediment loss very well probably due to insufficient number of measured events and low measured sediment loss. The measured runoff was 57% higher for CW watersheds compared to AgB watersheds. The measured sediment loss was 95% higher for CW watersheds compared to AgB watersheds. After calibrating and validating the model, it was run for long-term scenario analyses for 10 years from 1999 to 2008. Simulated buffer width had a significant influence on runoff. Simulated runoff decreased by 24% when the buffer width was doubled compared to losses associated with the measured buffer width. Simulated runoff from the CW watersheds was 11% higher with double stocking density (relative to measured density) compared to AgB watersheds with double stocking density. With half stocking density (relative to measured density), the AgB watershed had 18% lower runoff compared to CW. Results from this study imply that establishment of agroforestry buffers on grazed pasture watersheds reduce runoff and sediment losses compared to control watersheds without buffers.     

Soil quality indicator responses to row crop,grazed pasture,and agroforestry buffer management

Soil enzyme activities and water stable aggregates have been identified as sensitive soil quality indicators, but few studies exist comparing those parameters within buffers, grazed pastures and row-crop systems. Our objective was to examine the effects of these land uses on the activities of selected enzymes (β-glucosidase, β-glucosaminidase, fluorescein diacetate (FDA) hydrolase, and dehydrogenase), proportion of water stable aggregates (WSA), soil organic carbon and total nitrogen content. Four management treatments [grazed pasture (GP), agroforestry buffer (AgB), grass buffer (GB) and row crop (RC)] were sampled in 2009 and 2010 at two depths (0 to 10- and 10 to 20-cm) and analyzed. Most of the soil quality indicators were significantly greater under perennial vegetation when compared to row crop treatments. Although there were numerical variations, soil quality response trends were consistent between years. The β-glucosaminidase activity increased slightly from 156 to 177 μg PNP g⁻¹ dry soil while β-glucosidase activity slightly decreased from 248 to 237 μg PNP g⁻¹ dry soil in GB treatment during 2 years. The surface (0–10 cm depth) had greater enzyme activities and WSA than sub-surface (10–20 cm) samples. WSA increased from 178 to 314 g kg⁻¹ in row crop areas while all other treatments had similar values during the 2 year study. The treatment by depth interaction was significant (P < 0.05) for β-glucosidase and β-glucosaminidase enzymes in 2009 and for dehydrogenase and β-glucosaminidase in 2010. Soil enzyme activities were significantly correlated with soil organic carbon content (r ≥ 0.94, P < 0.0001). This is important because soil enzyme activities and microbial biomass can be enhanced by perennial vegetation and thus improve several other soil quality parameters. These results also support the hypothesis that positive interactions among management practices, soil biota and subsequent environmental quality effects are of great agricultural and ecological importance.     

Farming systems research for agroforestry extension

Farming systems research and extension (FSRE), as used by the global Association for Farming Systems Research-Extension, applies to a family of methodologies used to generate, evaluate and disseminate agricultural technologies in association with farmer participation. FSRE shares many attributes with Diagnosis and Design as practiced in agroforestry. The history of FSRE is traced from 1965 to the present, showing the formalization of the methodology and its critical use in sustainable agricultural technology development. In on-farm research, a primary basis for FSRE, research and extension merge in practice. The definition of recommendation domains (a fundamental concept of FSRE) is based on analysis and interpretation of multi-environmental research results as evaluated by varied criteria.In this paper, we present the results of three research projects to demonstrate the nature of farmer criteria for evaluation. Modified Stability Analysis (MSA) is used to demonstrate the relationship of on-farm research to specific extension messages. Design of on-farm research to make it amenable to analysis by MSA is discussed.Florida Agricultural Experiment Station, Journal Series No. R-03113.     

Tree root characteristics as criteria for species selection and systems design in agroforestry

This literature review presents information about the role of tree root systems for the functioning of agroforestry associations and rotations and attempts to identify root-related criteria for the selection of agroforestry tree species and the design of agroforestry systems. Tree roots are expected to enrich soil with organic matter, feed soil biomass, reduce nutrient leaching, recycle nutrients from the subsoil below the crop rooting zone and improve soil physical properties, among other functions. On the other hand, they can depress crop yields in tree-crop associations through root competition. After a brief review of favourable tree root effects in agroforestry, four strategies are discussed as potential solutions to the dilemma of the simultaneous occurrence of desirable and undesirable tree root functions: 1) the selection of tree species with low root competitiveness, eventually supplemented by shoot pruning; 2) the identification of trees with a root distribution complementary to that of the crops; 3) the reduction of tree root length density by trenching or tillage; and 4) the use of agroforestry rotations instead of tree-crop associations. The potential and limitations of these strategies are discussed, and deficits in current understanding of tree root ecology in agroforestry are identified. In addition to the selection of tree species and provenances according to root-related criteria, the development of management techniques that allow the manipulation of tree root systems to maximize benefit and minimize competition are proposed as important tasks for future agroforestry research.     

Evaluating Alnus acuminata as a component in agroforestry systems

The combination of alder (Alnus acuminata H.B.K.) with pastures, mainly Pennisetum clandestinum (kikuyu grass) and P. Purpureum (elephant grass) is a traditional practice in Costa Rican dairy highlands (between 1300–2500 masl). People believe that the pasture grows greener under the trees [Combe, 1979]. Alder is not only advantageous for fodder production but also for fuelwood and timber. It produces an additional source of income to the small farmer. The potential area for this association was first estimated in 60,000 ha [Combe, 1979], but more recent estimations give figures of around 50,000 ha, including one third of this area in pastures already planted with alder [Canet, 1985]. The question of whether the species may have potential for use in agroforestry systems in countries other than Costa Rica and research needs for the species are also discussed.     

Agroforestry and grass buffer effects on water quality in grazed pastures

Conservation practices including agroforestry and grass buffers are believed to reduce nonpoint source pollution (NPSP) from pastured watersheds. Agroforestry, a land management practice that intersperses agricultural crops with trees, has recently received increased attention in the temperate zone due to its environmental and economic benefits. However, studies are limited that have examined buffer effects on the quality of water from grazed pastures. Six treatment areas, two with agroforestry buffers, two with grass buffers, and two control treatments were used to test the hypothesis that agroforestry and grass buffers can be used to effectively reduce NPSP from pastured watersheds. Vegetation in grass buffer and pasture areas includes red clover (Trifolium pretense L.) and lespedeza (Kummerowia stipulacea Maxim.) planted into fescue (Festuca arundinacea Schreb.). Eastern cottonwood trees (Populus deltoides Bortr. ex Marsh.) were planted into fescue in agroforestry buffers. Soils at the site are mostly Menfro silt loam (fine-silty, mixed, superactive, mesic Typic Hapludalfs). Treatments were instrumented with two-foot H flumes, water samplers, and flow measuring devices in 2001. Composite water samples were analyzed for sediment and total nitrogen after each runoff event to compare treatment differences. Treatments with agroforestry and grass buffers had significantly lower runoff volumes as compared to the control. The loss of sediment and total nitrogen were smaller for the buffered treatments. The results of this study suggest that establishment of agroforestry and grass buffers help reduce NPSP pollution from pastured watersheds. It is anticipated as trees grow and roots occupy more soil volume, the reduction in N in runoff will increase on the agroforestry watershed.     

Planning optimal economic strategies for agroforestry systems

Design of agroforestry systems requires a land management planning process that clearly specifies wants, needs and objectives along with the land's suitability for potential agroforestry practices. Within this planning process economic analysis can be used to analyze agroforestry alternatives to help determine the proper system to apply. Specifically, production economics coupled with capital theory and valuation techniques can provide measures of economic performance in terms of present net values, benefit-cost ratios and internal rates of return. These economic performance measures can be used to determine the best joint production level for a particular agroforestry practice. Once these best combinations have been defined, linear programming can be applied using these best joint production combinations as decision variables along with considering a wide range of additional constraints and requirements. A hypothetical example is used to illustrate the planning process and how these economic tools can be combined as a package to help determine optimal agroforestry strategies.     

Microbial community diversity in agroforestry and grass vegetative filter strips

Vegetative filter strips (VFS) have long been promoted as a soil conservation practice that yields many additional environmental benefits. Most previous studies have focused primarily on the role of vegetation and/or soil physical properties in these ecosystem services. Few studies have investigated the soil microbial community of VFS. Therefore, we examined potential differences in soil microbial community characteristics of claypan soil planted to VFS with differing vegetation and a traditional row-crop system in a maize–soybean rotation. Samples were tested for soil microbial function and community structure using dehydrogenase and fluorescein diacetate (FDA) hydrolysis enzyme assays and phospholipid fatty acid (PLFA) analysis, respectively. The grass VFS soil exhibited the greatest dehydrogenase activity levels and FDA activity was greater in the grass and agroforestry (i.e., tree–grass) VFS soils relative to the cropland soil. The PLFA analysis revealed community structural differences underlying these functional differences. The agroforestry VFS soil was characterized by a greater proportion of total bacteria, gram-negative bacteria, anaerobic bacteria and mycorrhizal fungi than the cropland soil. The grass VFS soil shared some characteristics with the cropland soils; but the grass VFS supported greater mycorrhizal fungi and protozoa populations. This work highlights differences in soil microbial function and community structure in VFS relative to cropland soil 12 years post VFS establishment. It also enhances our fundamental knowledge regarding soil microorganisms in VFS, which may aid in explaining some ecosystem services provided by VFS (e.g., decomposition of organic agrichemicals).     

Improving multipurpose tree and shrub species for agroforestry systems

With the aid of an example of ICRAF's tree improvement research programme for the highlands of Eastern and Central Africa, a logical approach to selection and breeding of multipurpose trees and shrubs in agroforestry context is proposed. Criteria for selection of high priority species are proposed. Some species of high potential for agroforestry development in Sub Sahara Africa are proposed. The necessary sequential research steps are discussed.     

Temporal analysis of agroforestry systems for rural development

Temporal analysis is introduced as a method to assess the suitability of agroforestry projects for meeting rural development objectives. This form of analysis provides a common base for examining social, economic, ecological, and managerial aspects of agroforestry systems.Temporal analysis begins by describing projects and the activities comprising them for both an agroforestry system and the local population. Factors constraining the sequence of activities are then examined. The assumptions and values regarding the past, present, or future are also analyzed for all groups involved in the agroforestry system. The range of goal oriented behavior affecting scale and duration of projects may be dependent on this time horizon.By understanding these factors, the changes in activities of a social system that may result from a proposed agroforstry innovation can be anticipated. The nature of these changes and their perception by the local population can be evaluated.     

An evaluation of agroforestry systems as a rural development option for the Brazilian Amazon

In the Brazilian Amazon mass deforestation has resulted from a sequenceof road building, extractive logging, and pasture development during the pastthree decades. Ranchers have consolidated small agricultural holdings, pushingfarmers to move to forest frontiers or urban fringes, prompting furtherdeforestation and social instability. In response to this conversion ofAmazonian forests, the authors sought to identify both economically viable andmore sustainable development alternatives within the Brazilian state ofPará. There, local farmers of Japanese descent have developed a varietyof agroforestry systems in which 10 to 20 hectare (ha) fields yieldincomes comparable to 400 to 1,200 ha pastures. In addition, suchcrop fields generate substantially more rural employment per hathan do pastures. Ongoing forest conversion to pasture is clearly not a productof sound economic decision making. Improved land zoning and public policiescould favor agroforestry over further pasture expansion, stabilizing ruralpopulations while helping to conserve the Amazon's remaining forests. This revised version was published online in June 2006 with corrections to the Cover Date.     

Toward a rationally robust paradigm for agroforestry systems

Because people need improved agroforestry and because there are perceived limitations in a largely scientific approach to agroforestry research and development in the past, an alternative paradigm to gaining knowledge for use in this area is suggested. It is an encompassing approach to gaining knowledge which we call the rationally robust paradigm, RRP. The paradigm has 11 components: 1. Concentrating on site-specific knowledge, often in a geographic information system; 2. being aware of the limited funds to achieve agroforestry objectives; 3. de-emphasizing induction and deduction, and their replacement by or addition of other epistemological bases; 4. accepting lower confidence levels for conclusions and subsequent action; 5. using estimates of median values; 6. using knowledge of the range limits of agroforestry phenomena and factors; 7. giving attention to the system's phenomenon of equifinality and its consequences; 8. de-emphasizing time as a factor in system analysis, and replacing it with other system phenomena; 9. using statistical regression techniques but simultaneously seeking to identify and use independent factors (e.g., solar radiation) that function significantly in many models; 10. appropriately using regression techniques emphasizing the use of hypothesized, often-non-linear relationships; and 11. operating in a conceptual clinical milieu. The paradigm is proposed for use throughout agroforestry.     

Black leaf streak disease and plantain fruit characteristics as affected by tree density and biomass management in a tropical agroforestry system

Black leaf streak disease (BLSD) affects both bananas and plantains. Anecdotal evidence suggests that when plantain is grown under shade in agroforestry systems, there is less damage from BLSD. In this study, BLSD severity and agronomic fruit characteristics of plantain were compared under high and low timber stand densities (TSD), and also under different crop management systems (mulching, burning, intercropping). By 11 months after planting, in high TSDs, plants had 1.2 more standing leaves, 1.5 more symptom-free leaves and a lower percentage of total leaf area attacked than in low TSDs. At harvest, plants in high TSDs had, on average, 1.4 more standing leaves than those in low TSDs. Percentage leaf area attacked by BLSD was 43.0 % in high TSD treatments, significantly lower than the 57.2 % in low TSD treatments. There was a significant and positive relationship between the number of leaves at flowering and dry fruit bunch mass for plantains grown under low TSD. However, there was no correlation between the number of leaves and fruit mass for the high TSD. The beneficial effects of shade in the high TSD, such as reduced severity of BLSD, were established. However, as there was bunch mass loss associated with reduced leaf production rates under the high TSD, a reduction in BLSD only partially compensated for this yield loss. Thus overall, at the high TSD, there was no yield gain from reduced BLSD.     

Medicinal and aromatic plants in agroforestry systems

Agroforestry Systems - A large number of people in developing countries have traditionally depended on products derived from plants, especially from forests, for curing human and livestock...     

Veterinary antibiotic sorption to agroforestry buffer,grass buffer and cropland soils

The potential of veterinary antibiotics (VAs) to impact human and environmental health requires the development and evaluation of land management practices that mitigate VA loss from manure-treated agroecosystems. Vegetative buffer strips (VBS) are postulated to be one management tool that can reduce VA transport to surface water resources. The objectives of this study were to (1) investigate oxytetracycline (OTC) and sulfadimethoxine (SDT) sorption to agroforestry buffer, grass buffer, and cropland soils, (2) evaluate differences in VA sorption to soils collected from different vegetative management and soil series, and (3) elucidate relationships between soil properties and VA sorption. Sorption/extraction isotherms for OTC were well-fitted by the Freundlich isotherm model (r ² > 0.86). OTC was strongly adsorbed by all soils and the VA was not readily extractable. OTC and SDT solid to solution partition coefficients (K _d) values are significantly greater for soils planted to VBS relative to grain crops. Significant differences in OTC and SDT K _d values were also noted among the soil series studied. Linear regression analyses indicate that clay content and pH were the most important soil properties controlling OTC and SDT adsorption, respectively. Results from this study suggest that agroforestry and grass buffer strips may effectively mitigate antibiotic loss from agroecosystems, in part, due to enhanced antibiotic sorption properties.     

Perennial pigeonpea: a multi-purpose species for agroforestry systems

Perennial pigeonpea is receiving considerable attention in India as a multi-purpose species for agroforestry systems. Its multiple uses include food, fodder, manure and firewood. Data on perennial pigeonpea, together with relevant information on shorter-duration genotypes, are reviewed in this paper. Growth of perennial pigeonpea, like that of medium-duration grain types (150 to 190 days) in intercropping systems with cereals, is slow during the first 3 to 4 months. Therefore, it requires minimum sacrifice in terms of yield of annual crops in the system during the first year and offers many of the benefits of tree species in subsequent years. Total dry matter production potential of perennial pigeonpea in peninsular India is more than 15 t ha⁻¹ year⁻¹ consisting of about 2.0 t of grain, 3.0 t of leaf litter, 9.0 t of stems and 1.0 t of residue made up of podwalls and twigs. In addition, pigeonpea improves soil fertility by nutrient cycling and biological nitrogen fixation. Susceptibility of pigeonpea to diseases and negative effects on growth of annual crops are the potential constraints in the semi-arid tropics. Some pertinent areas for further research are proposed. Submitted as ICRISAT Journal Article No. 917 for ‘Agroforestry Systems’.